Ammonium
Molybdate:
1. Preparation of 0.5M, 1
N.
Mix
well 72 g of pure MoO5 (or 81 g of H2MoO4) with 200 ml of water, and add 60 ml
of conc. ammonium hydroxide. When solution is complete, filter and pour
filtrate, very slowly and with rapid stirring, into a mixture of 270 ml of
conc. HNO3 and 400 ml of water. Allow to stand over night, filter and dilute to
1 liter.
2. The reagent is prepared as two solutions which are
mixed as needed, thus always providing fresh reagent of proper strength and
composition. Since ammonium molybdate is an expensive reagent, and since an
acid solution of this reagent as usually prepared keeps for only a few days,
the method proposed will avoid loss of reagent and provide more certain results
for quantitative work.
Solution 1:
Dissolve 100 g of ammonium molybdate (C.P. grade) in 400 ml of
water and 80 ml of 15 M NH4OH. Filter if necessary, though this seldom has to
be done
Solution 2:
Mix 400 ml of 16 M nitric acid with 600 ml of water.
For
use, mix the calculated amount of solution 1 with twice its volume of solution
2, adding solution 1 to solution 2 slowly with vigorous stirring. Thus, for
amounts of phosphorus up to 20 mg, 10 ml of solution 1 to 20 ml of solution 2
is adequate. Increase amount as needed.
